This protocol is part of a multi-center study, being performed in five GCRCs across the country. It's aim is to phenotype sibling pairs with hypertension on the basis of multiple variables; including insulin resistance, salt sensitivity, red blood cell Na+-Li+ counter-transport, and angiotension-adrenal modulation. Enrollment of patients continues. The measurements are beginning to be made, and will define the degree to which the various phenotypic expressions of hypertension are overlapping.